Currently, the clinical diagnosis of skin disease is generally accomplished by visual inspection under white light illumination. In this process, the reflectance pattern of a skin lesion is examined. Visual diagnosis alone may not be particularly accurate for the early detection of skin cancer since many skin conditions have a similar appearance under white light. Therefore, when a suspect lesion is identified by visual examination, a biopsy is often performed for a definitive diagnosis. Not only is it crucial to diagnose skin pre-cancer or cancer at its early stage when it is curable, it is also important to improve the clinical diagnosis of suspect skin lesions so as to avoid unnecessary skin biopsies.
Several approaches have been tried to improve dermatologic diagnosis. Digital processing of reflectance images has been intensively investigated recently. Although reflectance imaging has led to improvements in registration, recording, and documentation of skin lesions, there has been little improvement in the diagnostic accuracy. The foregoing approach does not provide any additional data to the physician making the visual assessment because it is still based on the reflectance pattern of a lesion under white light illumination which is essentially the same pattern a human observer sees.
An alternative approach is ultraviolet UV or infrared IR photography which extends the visual perception of a physician to UV or IR reflectance patterns. However, the inconvenience due to delays in film image processing renders this technique impractical for everyday use.
A further alternative approach that is already in widespread medical use involves a "Wood's lamp" which consists of a mercury discharge lamp equipped with a filter that absorbs visible light, and transmits UVA light with a 365 nanometer peak. When using this device to assist in skin diagnosis, the eye serves as both the detector and the long pass filter. The eye is not sensitive to UV light, but is sensitive to visible fluorescent light. The "Wood's lamp" must be used in a darkened room, where the physician can see an image of a fluorescing disease site. The "Wood's lamp" is useful for the diagnosis of skin conditions such as tinea capitis, tinea versicolor erythrasma, and some pseudomonas infections, as well as aiding in the detection and diagnosis of hypopigmented lesions.